1. Field of the Invention
The present invention relates to disk brake devices that have a pair of pads adapted to be pressed against a brake disk, including disk brake devices that have a right pair of pads and a left pair of pads that are adapted to be respectively pressed against a vehicle's right-side wheel brake disk and a vehicle's left-side wheel brake disk.
2. Description of the Related Art
In general, a vehicle, such as an automobile, disk brake device includes a right brake disk (a disk is also known as a rotor) and a left brake disk respectively connected to a right wheel and a left wheel. The disk brake device can have a right pair of pads and a left pair of pads that are adapted to be pressed against the right brake disk and the left brake disk. Each pair of right and left pads includes an inner pad and an outer pad. For example, the right pair of pads has an inner pad disposed on the left side of the brake disk and an outer pad disposed on the right side of the brake disk. The left pair of pads is configured oppositely to the right pair of pads.
Heretofore, various countermeasures have been proposed in the known art in order to reduce the squealing sounds produced by the pads of a disk brake device. For example, Japanese Laid-Open Utility Model Publication No. 6-69459 teaches a pad configured to reduce such squealing sounds. The pad of this publication includes a friction member and a back plate that supports the friction member from the back side. A recess is formed in the back plate and extends in a vertical direction (the radial direction of the brake disk). The recess enables the back plate to have a tendency to be easily bent about the recess. Therefore, during the braking operation, the pad may be bent in order to facilitate the pressing of the central portion of the pad upon the brake disk. For this reason, the central portion of the pad may still be pressed against the brake disk even if the central portion of the pad has become slightly concave due to uneven wearing of the pad. Therefore, the friction member may apply relatively uniform surface pressure, reducing the squealing sounds produced by the pad.
However, squealing sounds of a pad may be produced due to various modes of vibration, as shown in FIGS. 4 to 6. FIG. 4 shows a typical first vibration mode. The first vibration mode can manifest in vibration about a single primary bending direction. For example, the primary bending direction shown in FIG. 4 is a bending of the pad about an area across the width of the pad. FIG. 5 shows a second vibration mode. The second vibration mode can manifest in vibration about a single primary twisting direction. Generally, the second vibration mode shown in FIG. 5 is a twisting about an area obliquely extending along the length of the pad. FIG. 6 shows a third vibration mode. The third vibration mode can manifest in vibration about secondary bending locations. As shown in FIG. 6, the secondary bending locations include two bending areas extending across the width of the pad. The third vibration mode involves vibration about each of the two bending areas.
It has been known that the first, second, and third vibration modes produce separate and distinct squealing sounds. The three squealing sounds, P1, P2, and P3, can each have different frequencies, as shown in FIG. 7.
The known pad of the above publication can effectively reduce the squealing sound produced by the first vibration mode, where the vibration occurs about a single primary bending direction. However, use of the known pad does not appear to effectively reduce the squealing sounds that may be produced in the second vibration mode, where the vibration occurs about a primary twisting direction.
In another type of known pad, a recess (slit) is formed in the face of the friction member. In particular, pads are known that have such a recess (or slit) extending along the face of the friction member. However, such a recess has generally been incorporated in order to remove powders that may be produce due to wear of the friction member. Therefore, the direction or orientation of the recess with regard to reducing vibration has typically not been considered as a design factor.